When growing requirements are imposed on “Internet of everything,” technologies related to Internet of Things are developing more rapidly. As an Internet of Things system, an NB M2M (Narrow Band Machine-To-Machine) system has an architecture similar to an existing cellular network. In this architecture, a terminal device performs data transmission according to scheduling by a base station.
In a common NB M2M system scenario, a base station may have multiple cells to cover terminal devices at different locations. When communicating with the base station, a terminal device needs to first obtain some information about a cell in which the terminal device is located. A physical cell identifier (PCI) is a type of relatively important cell information.
Existing NB M2M systems are designed by mainly referring to a Long Term Evolution (LTE) system. A PCI of each cell in the LTE system is indicated by using a PSS (Primary Synchronization Signal) sequence and an SSS (Secondary Synchronization Signal) sequence. Specifically, a base station has three cells. The three cells are identified by using three different PSS sequences; and different base stations in the LTE system are identified by using 168 SSS sequences. As a result, the cells in the LTE network are identified by using 504 different PCIs. When receiving broadcast information sent by the base station, a terminal device performs time-frequency synchronization on the broadcast information and the 3 PSS sequences and the 168 SSS sequences stored in the terminal device, to obtain a PCI of a cell in which the terminal device is located.
In an NB M2M system, if a PCI design method same as that of the LTE system is used, a terminal device of the NB M2M system usually consumes more power when obtaining the PCI. This is contrary to an original low-cost and low-power-consumption design of the terminal device of the NB M2M system. One feasible design method is to set a smaller quantity of PCIs for a cell in the NB M2M system (that is, to set a smaller quantity of SSS sequences that are used to identify a base station in the NB M2M system), so that the quantity of SSS sequences stored in the terminal device is reduced. This simplifies a time-frequency synchronization process performed by the terminal device, so as to reduce cost and power consumption of the terminal device.
However, when a smaller quantity of PCIs for the cell in the NB M2M system is set, a probability that cells with a same PCI occur within a specific area is higher than that in a case with a larger quantity of PCIs. When the terminal device simultaneously receives data sent by the base station to the cells with a same PCI, the terminal device is unable to normally obtain information from the received data.